http://www.clubsnap.com/forums/reviews/1183580-review-billingham-hadley-small-shoulder-bag.html
Based on Silas review, Hadley Small can fit iPad.
I'd actually say that the Pro would be better. Sure, there will probably be an extra compartment unused, but you could fill it up with a small bottle or umbrella or both at times. Or just dump the wallet, handphone, passport, keys there. The front pockets can just remain for camera accessories such as batteries, etc. Certainly no one goes around with just one battery?
Another reason why I support the Pro is the grab handle... I know it's not THAT important but it's a small price to pay when moving the bag over short distances or simply holding it up to unzip the rear compartment. (Btw, does the Hadley small have a rear compartment?)